VARIATIONS IN THE BLOOD COMPOSITION OF NON-PREGNANT HEREFORD AND ANGUS HEIFERS FED INDIVIDUALLY IN CONFINEMENT ON TWO LEVELS OF ENERGY INTAKE

Abstract

Ten Hereford heifers and 10 Angus heifers were given a high energy diet and equal numbers of Hereford and Angus heifers a low energy diet in individual pens from an average age of 476 day s. After 140 day s, one-half of the heifers of each breed on each energy level were changed to the other level while the other half of the heifers remained on the same level for a further 140 days. Blood samples were taken each 28 days to determine the influence of date of sampling and energy intake on levels of organic and inorganic constituents in the blood. Daily gains averaged 0.2 kg on the low and 0.6 kg on the high energy intake. Levels of all the blood constituents measured differed significantly (P < 0.05) between some of the sampling days. Levels of packed cell volume, whole blood glucose and corrected glucose were highest in January, which was the coldest day of blood sampling, and remained high until April. Serum potassium levels declined over the period of the trial. Total serum cholesterol levels increased (P < 0.01) and plasma nonesterified fatty acid levels decreased (P < 0.05) when energy intakes were increased. Serum phosphorus levels increased (P < 0.05) when dietary phosphorus intakes increased. Angus heifers had higher (P < 0.05) corrected glucose levels in their blood than did Hereford heifers.